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The one thing that always catches me is that, when transcoding, by default, it only includes the first video track and the first audio track. If you have a file that contains multiple (multiple audio tracks are the most common example), you can add "-map 0" which means "include all tracks".

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It's not the first tracks. Read http://ffmpeg.org/ffmpeg.html#Stream-selection

Many target formats do not support data sit subtitle streams, should de original contain then. So when using map 0, best then explicitly exclude those if you don’t care for them via -0:d? and -0:s? as we found out the hard way at Transloadit

In this situation, probably simpler and clearer to just do -map 0:v -map 0:a to just select the video and audio tracks in the first place.

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